As the demand for improved semiconductor device performance continues to increase, so too does the need for improved semiconductor device characterization techniques. Semiconductor wafers, such as silicon wafers, play an important role in the fabrication of device structures. Such device structures include, but are not limited to, semiconductor structures for light emitting diodes (e.g., MOCVD grown structures), low energy implanted and laser annealed ultra-shallow junctions, semiconductor solar cells and p-n junction thin film solar cells. Improved monitoring of p-n junction device quality is critical in the development of advanced semiconductor device fabrication. A variety of monitoring and measurement techniques are currently employed to monitor device quality. Currently utilized tracking techniques include a variety of non-contact and contact measurement techniques.
Current-voltage (I-V) curves are commonly used when characterizing diode device performance. I-V curves are typically measured with source-measure units that source a predetermined current and sweep this current over a pre-determined range. The voltage required to force the current through the given device is recorded, and the source-measure unit reports a set of paired data-points yielding an I-V curve. I-V curves are very important to device researchers and manufacturers because the measured data can be fit with known equations, which describe the behavior of the given devices. Parameters can be extracted from the fit and offer meaningful insight into the quality of measured devices, as well as potential future reliability. I-V curves are generally limited in the prior art because the use of a source-measure unit for device testing requires finished devices. This is particularly problematic because many junction diode based devices acquire their inherent electronic functionality following front-end processing steps, with additional expensive backend steps required before the devices are finished and before the devices can be tested.
One specific measurement technique includes a four-point probe technique. Advanced 4PP techniques may allow for the measurement of sheet resistance and conductance measurements of p-n junctions. The use of a four-point probe (4PP) to measure sheet resistance and conductance of p-n junctions is generally described in U.S. Pat. No. 7,714,596, issued on May 11, 2010, which is incorporated herein by reference in the entirety. Four-point probe techniques suffer from a variety of drawbacks. For example, four-point probe technique are difficult to implement in a non-destructive inline capacity. Further, p-n junction conductance is generally measured at low reverse bias and depends primarily on shunt resistance, while I-V curves characteristic of real devices (e.g., LEDs, solar cells and the like) depend primarily on recombination characteristics at high forward bias conditions.
Additional techniques for measuring I-V curves and electroluminescence include spring loaded probe contact techniques. Spring loaded contact measurement techniques are described generally in U.S. Pat. No. 7,679,381, issued on Mar. 16, 2010; U.S. Patent Publication No. 2013/0043875, filed on Dec. 21, 2011; and U.S. Patent Publication No. 2013/0046496, filed on Dec. 21, 2011, which are each incorporated herein by reference in the entirety. The spring loaded probe technique is based on the measurement of I-V curves and electroluminescence intensity stimulated by forward voltage, which is applied to the spring loaded probe with reference to the bottom n-layer of the junction, connected through the edge of the wafer with a second probe. This technique also suffers from a number of disadvantages. One of the primary disadvantages of this techniques includes the failure to account for the lateral current in the p-n junction layers, which is dependent on sheet resistance, and leads to a reduction in the measured current density, especially under reverse bias. In addition, this method suffers from the presence of measurement artifacts related to the contamination, high contact resistance, alignment difficulties, the present of particles and the like.
It is evident that the prior art includes a number of deficiencies. Therefore, it would be desirable to provide a method and system that cure these deficiencies of the prior art identified above.